Researches on the marine algal flora in the middle part of the Japan Sea coast of Honshu including Sado Isl. were carried out by the writer at the 19 stations shown in the previous report in 1967, 1977, 1978 and 1979 (At and Off Tassha, Sado Isl., July 27-30). As a result of the present researches, the writer could collect 281 spp. of marine algae including 30 spp. of Cyanophyta, 34 spp. of Chlorophyta, 77 spp. of Phaeophyta reported in the previous paper, and 141 spp. of Rhodophyta belonging to 68 genera and 28 families which are reported together with the two spp. of seagrasses in this paper this time.
The following 8 spp. marked with ◎ in the list are new to the Japan Sea : Goniotrichum cornu-cervi, Pikea californica, Griffithsia corallina, Wrangelia tagoi, Polysiphonia fruticulosa, Polysiphonia tongatensis, Hypoglossum geminatum and Dasyopsis plumosa. The following 3 spp, marked with ○ are new records to the middle part of the Japan Sea coast of Honshu : Gracilaria incurvata, Binghamiella callfornica, Hemineura schmitziana. Microcladia dentata and Erythroglossum repens marked with ※ are new entries to the marine flora of the Sado Isl..